There is a rapid progress in performance and diversification in recent years of a variety of electronic apparatuses such as cellular phones and personal computers, and the like. In pace with the progress, a strong demand exists for means to make control panels such as push buttons legible and operable even in a dark environment. There is thus an increase in number of apparatuses that illuminate control panels using lighted switch units and lighted switch sheets provided with various kinds of light-emitting devices. A lighted switch unit of such kinds of the prior art will be described hereinafter with reference to FIG. 6.
FIG. 6 is a cross sectional view of a lighted switch unit of the prior art, wherein wiring board 1 provided with a plurality of wiring patterns (not shown in the figure) formed on both upper and lower surfaces also has a plurality of center stationary contacts 2A as well as a plurality of outer stationary contacts 2B formed on the upper surface.
Each of movable contacts 3 made of resilient thin metal plate has generally a hemispherical shape with a convexed center, and it is affixed on wiring board 1 with tape 4 backed by adhesive (not show in the figure) in a manner that a bottom peripheral edge is positioned on outer stationary contact 2B.
Light emitting diodes 5 (hereafter referred to as “LED”) are mounted also on the upper surface of wiring board 1 in the vicinity of movable contacts 3.
Each push button 6 made of dark-colored insulating plastic has indicator face 6A of translucent, milk-white or the like colored material marked with a character, a symbol, a pictorial sign or the like on the upper surface, and depressing boss 6B on the lower surface. Depressing boss 6B protrudes downward and a bottom end of it abuts upon a top center portion of movable contact 3 through tape 4. A plurality of these push buttons 6 project through openings 7A provided in casing 7 formed of insulating plastic of an electronic apparatus. The lighted switch unit having the structure as described above is used for an electronic apparatus of the prior art.
Description will be provided next of an operation of the lighted switch unit of the prior art having the above-described structure.
When any of push buttons 6 is pushed downward, a bottom end of depressing boss 6B depresses the top center portion of the corresponding movable contact 3, causing it to invert with a click feeling. The inversion of movable contact 3 causes a lower center surface of it to contact with center stationary contact 2A, and completes an electrical connection between center stationary contact 2A and outer stationary contact 2B through movable contact 3.
Next, when the depressing force is removed from push button 6, a resilient restoring force of movable contact 3 disconnects the lower center surface from center stationary contact 2A, and pushes back push button 6 upward at the same time to restore it into the original state shown in FIG. 6.
In addition, a predetermined operation causes a plurality of LEDs 5 to emit light for illumination of push buttons 6 from the underside, to help a user to locate any of push buttons 6 and see the characters and the like on indicator faces 6A easily even in a dark environment.
In the above-described lighted switch unit of the prior art, however, a number of LEDs 5 for illuminating push buttons 6 needs to be increased if the electronic apparatus has a large number of push buttons 6 due to high performance with a wide variation of uses. This results in an increase in number of components as well as a time required for assembly, which gives rise to a problem of high cost.